Electric circuit utilizing an adjustable and resettable fuse



y 9, 1967 0. K. NILSSEN 3,319,128 I ELECTRIC CIRCUIT UTILIZING ANADJUSTABLE AND RESETTABLE FUSE Filed Nov. 19, 1964 FEE-=4.

OLE K. NILSSEN lNVENTOR ATTOR/V VS United States Patent 3,319,128ELECTRIC CIRCUIT UTILIZING AN ADJUSTABLE AND RESETTABLE FUSE Ole K.Nilssen, Livonia, Mich., assignor to Ford Motor Company, Dearhorn,Mich., a corporation of Delaware Filed Nov. 19, 1964, Ser. No. 412,367 8Claims. (Cl. 317-54) This invention relates to an electric circuit inwhich there is employed a reliable and inexpensive electromagnetic fusethat may be both adjustable and resettable.

In automotive vehicles and other applications, there is need for anelectrical circuit in which a reliable and inexpensive fuse that is bothadjustable and resettable can readily be employed. This inventionprovides such an electrical circuit and fuse.

In the invention, a magnetic reed relay or switch is employed that has apair of reeds positioned in series with the power source and the load tobe supplied by this source. A winding connected in series with the powersource and the load is positioned around the reeds. A permanent magnetaxially polarized in the direction of the reeds is also positionedaround the reeds and the magnetomotive force of this permanent magnet isopposite to the magnetomotive force furnished by the current that flowsthrough the Winding from the power source.

The permanent magnet provides a magnetic bias on the reeds so that oncethe reeds are closed they will remain closed. If, however, the currentflowing through the winding reaches a predetermined level at which themagnet-emotive force of the permanent magnet is reduced to the pointwhere the magnetomotive force on the reeds is no longer large enough tomaintain the reeds in the closed position, the reeds will then open andthe circuit to the load will be broken.

The reeds may be reclosed by shifting the permanent magnet in adirection toward the junction position of the reeds to increase themagnetomotive force on the reeds to the point where they will again beclosed.

To adjust the current level at which the reeds open, the permanentmagnet may be moved in an axial direction to adjust the magnetomotiveforce on the reeds that tend to keep them closed, or the winding whichsupplies the subtractive magnetomotive force bias may be moved in anaxial direction.

To initially close the reeds of the magnetic switch or relay, thepermanent magnet may be momentarily moved into such a position that themagnetic bias or magnetometive force is large enough to close the reeds.It must thereafter be returned to the proper position, however, toprovide the correct fusing action. It is also possible to provide anextra winding around the magnetic relay or switch in which current ismomentarily applied so as to increase the magnetic bias or magnetomotiveforce sufficiently to close the reeds. This winding may also beenergized to reset the magnetic reed switch.

To open the magnetic reed relay or switch, short of drawing too muchload current, the permanent magnet may be shifted axially momentarily ina direction to decrease the magnetomotive force applied to the reeds bythis magnet, or current could be applied to the extra winding previouslydescribed so as to decrease the magnetic bias or magnetomotive force onthe reeds.

An object of the present invention is the provision of an electriccircuit which includes a simple and reliable fuse element that may beadjustable and resettable.

Another object of the invention is the provision of an electric circuitthat includes a simple and reliable fuse element that may also beadjustable and resettable.

Other objects and attendant advantages of the present invention may bemore readily realized as the specification 3,319,128 Patented May 9,1967 is considered in connection with the attached drawings in which:

FIGURE 1 is a circuit diagram of one embodiment of the invention, and

FIGURE 2 is a circuit diagram of another embodiment of the invention.

Referring now to the drawings in which like reference numerals designatelike parts throughout the several views thereof, there is shown inFIGURE 1 a source of electrical energy or battery 10 having its positiveterminal 11 connected through lead 12 to one reed 13 of a magnetic reedrelay or switch 14. The other reed 15 of the magnetic reed relay orswitch 14 is connected through lead 16 to one terminal of a winding orelectromagnetic means 17. The other terminal of the winding orelectromagnetic means 17 is connected through lead 18 to a load 21. Theload in turn is connected through lead 22 to the negative terminal 23 ofthe battery or source of electrical energy 10. A switch 20 may bepositioned in the lead 12 to control the energization of the load 21.

The magnetic reed relay or switch 14 is of standard construction inwhich the reeds 13 and 15 will close upon the application of apredetermined magnetomotive force. The magnetic reed relay or switch 14has hysteresis characteristics in which the magnetomotive force requiredto keep the reeds closed after they have once been closed is less thanthe force required for closing.

To provide a magnetic bias or magnetomotive force for closing the reeds13 and 15, a permanent magnet 24 that may take the form of a ceramiccylindrical permanent magnet polarized in an axial direction, ispositioned over the reed relay or switch 14. This permanent magnet 24engages the cylindrical housing of the reed relay or switch in a snugfit and is movable axially on the housing against the friction forcedeveloped between the housing and the magnet.

The winding 17 is wound on the magnetic reed relay or switch 14 in adirection such that current through it will create a magnetomotive forcethat opposes the magnetomotive force of the permanent magnet 24.

In the operation of the circuit shown in FIGURE 1, the permanent magnet24 is shifted axially'upon the housing of the magnetic reed relay orswitch 14 toward the junction of the two reeds 13 and 15. When themagnetomotive force across the open reeds 13 and 15 becomes largeenough, the reeds will close and the permanent magnet 24 is shifted backto the position on the housing to provide proper fusing action. Thisposition must be such that when the current through the winding 17 orelectromagnetic means becomes large enough to open the reeds, that themagnetomotive force on the reeds supplied by the permanent magnet 24 isnot sufficiently large to reclose the reeds 13 and 15 when the currentthrough the winding 17 or electromagnetic means is interrupted.

It can be readily appreciated that the permanent magnet 24 may beshifted axially to adjust the current level at which the reeds 13 and 15open. Also to open the reeds 13 and 15 short of drawing too much currentthrough the load 21 or opening the switch 20, the permanent magnet 24may be shifted momentarily to the left in FIG- URE 1.

It can be readily appreciated that when current through the load 21rises to a certain predetermined level in which the magnetomotive forceof the winding 17 reduces the m-agnetomotive force applied by thepermanent magnet 24 on the reeds 13 and 15 to a predetermined level,that the reeds 13 and 15 will open, thereby interrupting current to theload 21. Thereafter, the reeds may again be closed and the fuse reset byshifting the permanent magnet momentarily toward the junction point ofthe reeds 13 land 15, or to the right as viewed in FIGURE 1.

Another embodiment of the invention is shown in FIG- URE 2. Thisembodiment of the invention is similar to the embodiment shown in FIGURE1 except that an additional winding or electromagnetic means 26 ispositioned about the magnetic reed relay or switch 14, and the permanentmagnet 24 is of the rubber based type. The purpose of the extra winding26 is to provide extra magnetomotive force on the reeds 13 and 15 toclose them initially and for reclosing them after opening due tooverload conditions rather than shifting the permanent magnet 24 as wasdone in FIGURE 1.

To provide this additional magnetomotive force, a push button switch 31has one terminal connected through lead 32 to the lead 12 and thepositive terminal 11 of battery 10. The other terminal of the pushbutton switch 31 is connected through lead 33 to one terminal of thewinding 26. The other terminal of the winding 26 is returned throughlead 34 and lead 22 to the negative terminal 23 of the battery 10. Thewinding is wound such that the energization of this winding through theactuation of push button switch 31 supplies a magnetomotive force in thesame direction as of that supplied by the permanent magnet 24; and ifthe reeds 13 and 15 are initially open, the pushing of this push buttonswitch will close them. The pushing of the push button switch 31 willalso provide a means for resetting the magnetic reed relay or switch 14should it open due to an overload condition in which current through theload 21 and winding 17 exceeds a predetermined level.

It can be readily appreciated that the operation of this circuit is verysimilar to that shown in FIGURE 1. Depression of the push button switch31 will close the reeds 13 and 15. An overload condition in whichcurrent through the winding 17 exceeds a predetermined level will causethe reeds 13 and 15 to open, thereby interrupting current through theload 21. The magnetomotive force applied by the permanent magnet 24 willbe insufiicient to close the reeds 13 and 15. The pushing of the pushbutton switch 31, however, will reset the reeds 13 and 15 into theclosed position to provide the resetting of the switch or relaymechanism.

In the circuit shown in FIGURE 2 as Well as the circuit shown in FIGURE1, the permanent magnet 24 may be shifted axially to adjust the initialmagnetic bias or magnetomotive force to be applied on the reeds 13 and15.

The present invention thus provides in an electric circuit a simple andreliable magnetic reed relay or switch that may be employed as a fusingelement in the circuit. Means are provided to reset the magnetic reedrelay or switch element should it open due to an overload condition andto provide an initial setting or adjustment.

It is to be understood that this invention is not to be limited to theexact construction shown and described, but that various changes andmodifications may be made without departing from the spirit and scope ofthe invention as defined in the appended claims.

I- claim:

1. An electric circuit comprising, a source of electrical energy, aload, a magnetic reed switch having a pair of reeds and a windingsurrounding said reeds, circuit means coupling said source of electricalenergy, said pair of reeds, said winding and said load in series, and acylindrical permanent magnet surrounding said reeds and polarized in anaxial direction, said cylindrical permanent magnet having sufficientmagnetomotive force to close said reeds, said winding being wound toproduce a magnetomotive force in the opposite direction from saidpermanent magnet when current flows therethrough whereby said reeds willopen interrupting current to said load when said current produces apredetermined magnetomotive force.

2. An electric circuit comprising, a source of electrical energy, aload, a magnetic reed switch having a housing, a pair of reeds mountedin said housing, a winding positioned on said housing about said reeds,circuit means coupling said source of electrical energy, said pair ofreeds, said winding and said load in series, a cylindrical permanentmagnet slidably mounted on said housing and having sufficientmagnetomotive force to close said reeds, said winding being wound toproduce a magnetomotive force in the opposite direction from saidpermanent magnet when current fiows therethrough whereby said reeds willopen interrupting current to said load when said current produces apredetermined magnetomotive force.

3. An electric circuit comprising, a source of electrical energy, aload, a magnetic reed switch having a housing, a pair of reeds mountedin said housing, a permanent magnet means positioned adjacent saidhousing and producing sufiicient magnetomotive force to close saidreeds, an electromagnetic means, means for connecting saidelectromagnetic means in series with said source of electrical energy,said pair of reeds and said load, said electromagnetic means producing amagnetomotive force in a direction to oppose the magnetomotive force ofsaid permanent magnet whereby said reeds will open interrupting currentto said load when said current produces a predetermined magnetomotiveforce.

4. An electric circuit comprising, a source of electrical energy, aload, a magnetic reed switch having a cylindrical housing, a pair ofreeds positioned in said housing and extending in a generally axialdirection with respect to said housing, a cylindrical permanent magnetmeans polarized in an axial direction positioned around said housing atone end thereof, said cylindrical permanent magnet means havingsufficient magnetomotive force and being positioned to close said reeds,an electromagnetic means positioned about said housing at the other endthereof, said electromagnetic means being connected in series with saidsource of electrical energy, said reeds and said load, saidelectromagnetic means being wound to produce a magnetomotive force thatopposes the magnetomotive force produced by said permanent magnet meansas current flows from said source of electrical energy through saidload, said electromagnetic means producing sufficient magnetomotiveforce to cause said reeds to open when the current therethrough reachesa predetermined value.

5. The electrical circuit of claim 4 in which said cylindrical permanentmagnet means is axially movable along ,said cylindrical housing toenable said reeds to be either opened or closed.

6. The electrical circuit of claim 4 in which said electromagnetic meansis axially movable along said cylindrical housing.

7. The electrical circuit of claim 4 in which both said cylindricalpermanent magnet and said electromagnetic means are axially movablealong said cylindrical hous- 8. The electrical circuit of claim 4 inwhich a second electromagnetic means is positioned about saidcylindrical housing and in which means are .provided for temporarilycoupling said winding in circuit with said source of electrical energyto produce a magnetomotive force in the same direction as saidcylindrical permanent magnet.

References Cited by the Examiner UNITED STATES PATENTS 2,509,590 5/1950Galt 317-154 X 2,923,791 2/1960 Cor-bitt et al. 335-153 3,204,059 8/1965Saaty 335l53,

FOREIGN PATENTS 81,023 8/1958 Italy.

MILTON O. HIRSHFIELD, Primary Examiner.

R. V. LUPO, Assistant Examiner.

1. AN ELECTRIC CIRCUIT COMPRISING, A SOURCE OF ELECTRICAL ENERGY, ALOAD, A MAGNETIC REED SWITCH HAVING A PAIR OF REEDS AND A WINDINGSURROUNDING SAID REEDS, CIRCUIT MEANS COUPLING SAID SOURCE OF ELECTRICALENERGY, SAID PAIR OF REEDS, SAID WINDING AND SAID LOAD IN SERIES, AND ACYLINDRICAL PERMANENT MAGNET SURROUNDING SAID REEDS AND POLARIZED IN ANDAXIAL DIRECTION, SAID CYLINDRICAL PERMANENT MAGNET HAVING SUFFICIENTMAGNETOMOTIVE FORCE TO CLOSE SAID REEDS, SAID WINDING BEING WOUND TOPRODUCE A MAGNETOMOTIVE FORCE IN THE OPPOSITE DIRECTION FROM SAIDPERMANENT MAGNET WHEN CURRENT FLOWS THERETHROUGH WHEREBY SAID REEDS WILLOPEN INTERRUPTING CURRENT TO SAID LOAD WHEN SAID CURRENT PRODUCES APREDETERMINED MAGNETOMOTIVE FORCE.